1. Field of the Invention
The invention relates to a connector for electrical equipment and, more particularly, to a high density electrical connector provided with protection from electrostatic discharge events.
2. Description of Related Art
It is well known that electrical devices are typically provided with at least one interface for electrical connection with other electrical devices. Generally, such interfaces are either a plug type connector, which is typically inserted into a similarly configured second connector to complete an electrical connection between the electrical contacts of the two, or a receptacle type connector, which typically receives a plug type connector to complete the electrical connection between the contacts. Recently, high density electrical connectors, both plug and receptacle type, which provide multiple low voltage electrical connections in a relatively small area, have become common, particularly in computer systems where large numbers of low voltage electrical connections are required. Each individual electrical connector included as part of a high density electrical connector typically includes an electrical contact providing an electrical connection with an electrical contact of a second connector and a signal pin which is used to connect the contact with an associated electrical device.
When connecting or disconnecting a first electrical device, for example a computer, to or from a second electrical device, for example a computer peripheral such as a printer, opposite charges on the two interfaces may result in an electrostatic discharge between the two. If the discharge propagates to a contact electrically associated with a semiconductor or other low power electrical device, the discharge could result in the destruction of the electrical device associated with the contact to which the discharge propagates. Furthermore, with the increased use of CMOS and other low power semiconductor components, the likelihood that electrostatic discharges will be destructive has increased. For example, expandable portable computers are typically provided with an external connector internally connected to the major electronic components of the portable computer, many of which are low power semiconductor components. Finally, any electrical equipment having an exposed connector risks destructive electrostatic discharges at any time.
In the past, the protection of electrical equipment from electrostatic discharges has been provided at the pin or component level. In such schemes, separate protection against electrostatic discharges would be provided for each component or pin deemed at risk. For example, a separate electronic voltage clamping device such as a metal oxide varistor (or "MOV"), a transient suppressor zener diode, an arc gap capacitor, a flash tube, a diode clamp circuit, or the like, would be installed, typically on the printed circuit board itself, to protect a low power component from voltage surges resulting from electrostatic discharges. While effective, protecting components from electrostatic discharge at the component level has become impractical to implement, particularly in multiple component circuits, due to cost and space constraints.
On the other hand, attempts to protect electrical equipment from electrostatic discharges at the connector level have been infrequent. One prior solution focussed on the insertion of extra metal blades which would project outwardly past the rows of contacts, typically mounted on shorter insulative blades, into a plug type connector. However, this prior solution added significantly to the cost of manufacturing a plug type connector. Furthermore, the proposed solution was not readily applicable to receptacle type electrical connectors and, as a result, electrostatic discharge protection has remained rare for receptacle type connectors. Finally, the use of additional blades merely for electrostatic discharge protection results is a highly inefficient use of connector space and is inconsistent with the modern trend toward increasingly higher density electrical connectors.
Outer shells constructed of a conductive material such as metal have also been used for providing electrostatic discharge protection for electrical connectors. However, an outer metal shell typically provides protection from electrostatic discharges only in the range of 8 to 20 Kv. In this relatively high voltage range, the length of the electrostatic discharge is sufficiently long such that the charge will jump to the object having the greatest charge potential, i.e., the outer metal shell. For electrostatic discharges at voltages below this range, however, the discharge length is considerably shortened. As a result, the discharge will often travel to the closest conductive object, typically a connector pin, rather than to the more distant but higher potential outer shell. Furthermore, the use of conductive outer shells for protection against electrostatic discharges, like the insertion of conductive blades, is inconsistent with the trend toward higher density electrical connectors. Increases in pin counts most often result in increasingly larger outer shells and, the larger the shell, the more likely that an electrostatic discharge will travel to an electrical contact, rather than to the outer shell.